Noise exists in an energy spectrum obtained in spectral measurement irrespective of the measured energy value. For a wavelength where the energy level is relatively close to noise due to the optical characteristics of a light source, the sensitivity characteristics of a detector, a high absorption of an object to be measured, or the like, the noise is greatly amplified when the energy spectrum is converted into an absorbance spectrum. As a result, the noise becomes greater than the original absorption information, causing the inconvenience of failing to provide a correct quantitative analysis.
The existence of noise greater than the original absorption information is also inconvenient for the processing of the absorbance spectrum. The reason is that the large amount of noise makes it impossible to use an automatic axial alignment function, for example, which is inconvenient.
In multivariate analysis, measured values for multiple wavelengths are used for calculation. In such calculation, also, the existence of large amounts of noise is inconvenient. The reason is that the large amounts of noise makes it impossible to perform correct quantitative analysis.
Conventionally, in spectral measurement, a multi-scanning averaging method and a moving average smoothing method are known as methods for reducing noise included in a spectrum. Quantitative analysis is not conventionally available for a wavelength having an excessively large amount of noise.
In spectral measurement, noise included in an energy spectrum is substantially constant irrespective of the energy value. However, noise included in an absorbance spectrum becomes greater as the original energy level becomes smaller.
In the multi-scanning averaging method, it takes a considerably long time to obtain absorption information. Moreover, the level of noise reduction is limited.
In the moving average smoothing method, it is impossible to reduce noise greater than the original absorption information. Moreover, there is even a possibility of deleting absorption information in a wavelength range where noise is small.
The object of the present invention is to provide a method and an apparatus capable of reducing noise included in an absorbance spectrum in spectral measurement.